How do I stay on n41 band on my trash can?

Have you identified the PCI for the n41 and n71 channels and located the tower(s) that broadcast on these? The signal change might be due to signal strength due to the proximity of your location with respect to each source. I can’t say with any certainty but there might be some relationship there. The n41 will not be able to travel as far as the longer n71 signaling so it might be if the n41 signal is lost and the n71 is available it then transitions. You might be able to locate the tower(s) with cellmapper.net and get a better feel for what is taking place. It would probably be worth the time to talk to T-Mobile support and explain how your router is acting and find out if there is work being done on the tower(s) in the area. They also could provide coordinates for the location(s) of the two signals. If your router is on the fringe of the n41 signal it might just not be able to hold it and then transitions to the n71 source. Having the metrics for each of the signals would possibly help. Knowing tower locations and distance to the source(s) would also help. If you have had it working for some time now and this is a new behavior it might be that T-Mobile engineers are working on equipment in the area. A call to find out could confirm that.

As users of the cellular solution we have few “hacks” available to us. The best defense is to know what you have. Once you have a better picture of solution maybe it will be easier to get it stable.

Thats good that it has taken focus on the single source. If the SNR is good and the RSRP are both strong enough it should be a nice solution. The n41 for sure will provide better bandwidth as long as it can get to the antennas on the router. From all the research I have done the SNR has a major impact. I worked in networking for 22 years so I understand the basics extremely well. If the signal to noise ratio is good to excellent that improves performance as there are fewer retransmissions due to packet loss and/or damage. It just makes sense. You might have a little lower signal power but if it is clean that can make all the difference. The n41 being a shorter, higher wavelength may not have the penetration but under reasonable conditions it can be a big win for the cost factor. Nothing will be perfect but T-Mobile is making some headway. 

I really believe many of the people that have cut over to the T-Mobile solution have their expectations a bit high. Going from a wired to a wireless/cellular solution is a pretty big jump in terms of technical demands. Many subscribers don’t understand the technology nor have a good idea how to figure it out. It does require a learning curve and persistence. I worked with both wired and wireless gear for many years but even with all my experience I had to research and think through the cellular solution to get it to work well here. It takes more effort than most users want to invest. Once you have it zoned in it is a pretty good solution for the cost. I hope you can keep your lock stable. 

The battery might, I say might, keep the cellular signal alive but if power goes out the wireless radios will for sure be taken down. Mine seems to behave as if there is a soft reset when the cellular signal falls. Once it is established again there is a delay prior to full communication is established. I keep mine on an APC 1500 UPS to keep it standing and filter any transient spikes that might ride the AC line. When I lived in CA we had PG&E and the power was so flakey I had a PC motherboard spiked and destroyed some time ago. After that I put all our electronic equipment on UPS systems. I still run three UPS systems here in TN. 

I am not so sure that T-Mobile doesn’t push software to the router when it has a new release. A support engineer told me when the router reboots it will take an update if available. From that I suspect they push the software updates with management software and if the router reboots then the new software load will be installed. I have been on several revisions of the software. A couple of weeks ago the 1.2103.00.0338 was installed on it. I discovered an authentication bug. I know beyond a shadow of a doubt that it is due to the router software as I had never seen the behavior before that was running. It is easy to trigger and I have tested and confirmed it with multiple browsers on Apple, Windows 10, and Linux Mint and Garuda Linux. The only way to avoid it is to not save or autofill credentials from the router web interface. If you do encounter it I did put a post up about it a few weeks ago. T-Mobile support said they would follow up with me on it but they never did. I am 100% sure the issue is with the 1.2103.00.0338 and the web interface. The values that will “change”, be inserted into the auto save window can ONLY come from the router. Just don’t save your “admin” authentication to the browser and it should be ok. If you do encounter it look at your passwords in the browser, remove the one saved, and restart the browser. Then authenticate with your last functional password for the admin account. If the browser pops the question to save the authentication, just say no. Better yet don’t give it the chance to go there.

I recall reading some T-Mobile information about the router reset. To really cold boot it you have to use not only the removal of the power but also use the button to turn it off. I believe the article, it might have been one of the FAQs, recommended pressing the button on the back of the can to turn it off and then disconnect the power to the router. After it sits for a minute or two the power should drain from the components and it should flush out the registers and cashed information. Upon power up it takes roughly 2 minutes before it brings up both the cellular and wifi radios. 

If you only pull the power it can still run on the battery and try to maintain the cellular radio. It cannot run the wifi radios with the battery alone. So, a cold reboot is a little more effort. I don’t know for sure if the reset from the web interface would ever achieve the same result. I doubt it. I am guessing that is a warm reboot where it does not drain down. Software vs. hardware reboot are not equal in all cases.

With that authentication bug I used Firefox, Chrome, Edge, Vivaldi, and Safari and used Apple, Linux, and Windows so I tested it pretty extensive. I even tested it with a T-Mobile support engineer online. If you don’s save the authentication and use autofill you will not hit it. If you do by chance then you can look at the password saved in the browser and see if it is what you though or not. Flush the browser and then you can get back in with what you know you used.

Like you I read somewhere but can’t recall where, the purpose of the battery is to preserve settings and not to provide full function. Supposedly you can move the device around and watch the signal quality bars for the best location and orientation. I think in reading numerous posts on the subject it is pretty well established the number of bars is not a worthwhile indication of signal quality or strength. In fact the few times I have had three bars rather than the normal two, I had a poorer signal.